1. Field of the Invention
The present invention relates to a battery pack case, and more particularly to a battery pack case having a protective circuit module adapted to avoid escaping out of a bare cell and gates properly arrayed in such a manner that, when forming the case, it has no unshaped part.
2. Description of the Related Art
In general, a battery pack includes a chargeable/dischargeable bare cell, a protective circuit module electrically connected to the bare cell to control charging/discharging and to interrupt the current in case of overcharging/over-discharging, a resin filling a gap between the bare cell and the protective circuit module to prevent the protective circuit module from detaching from the bare cell, and a case containing the bare cell, the protective circuit module, and the resin therein.
A method of manufacturing a battery pack includes: electrically connecting a lead to the positive electrode of the bare cell and electrically connecting a PTC thermistor to the negative electrode thereof. The protective circuit module is again electrically connected to the lead and the PTC thermistor. A gap between the protective circuit module and the bare cell is filled with a resin to mechanically attach them so that the protective circuit module does not detach from the bare cell. The bare cell, the protective circuit module, and the like are contained within a case. The case is integrally molded using another resin together with the bare cell, the protective circuit module, and the resin. Alternatively, upper and lower cases are separately provided and, after placing the bare cell and the protective circuit module between them, are attached together.
However, such a battery pack has a problem in that, since a gap can be created between the bare cell and the protective circuit module even after placing them within the case or since they can detach from each other, a resin must be used to fill the gap between the bare cell and the protective circuit module in a difficult process to attach them to each other. During the resin filling process, various electronic components on the protective circuit module can be easily damaged and the lead and the PTC thermistor, which have previously been connected to each other, can detach from each other.
The PTC thermistor increases its resistance value when the temperature reaches about 70-80° C. and interrupts the current flowing through the circuit. Once it is actuated, its resistance value does not drop to the exact original value or the device characteristics degrade, even when the temperature returns to a normal range. Since the resin has a temperature of about 150° C. when filling the gap between the bare cell and the protective circuit module, the PTC thermistor is very likely to be actuated and degrade its characteristics.
In order to solve this problem, the PTC thermistor can be arranged on the outer periphery of the bare cell rather than between the bare cell and the protective circuit module. Then, the PTC thermistor is exposed to the danger of colliding with other objects and being damaged by them during manufacturing processes. The thickness of the PTC thermistor must also be taken into account when manufacturing the case. This makes the manufacturing processes complicated and increases cost.
In addition, a separate mold is necessary to fill the gap between the protective circuit module and the bare cell with a resin. This further increases the manufacturing cost of the battery pack and, as the processes become more complicated, the defect ratio increases.